For example, a system mentioned at the outset is known from DE 44 39 074 A1. According to this document, all radio tags must be in their active state at the time a preamble is sent out, so as to enable a synchronous data transmission to the radio tag in time windows allocated thereto. This measure is associated with a low energy and system efficiency. Further known from WO 2010/004349 A1 is a system in which the radio tags are allocated to individual time slots. For purposes of synchronization with the communication station, the latter sends out a preamble. This preamble contains several data packets, which indicate a deviation from a reference instant for the synchronous state between the communication station and radio tag. At an instant that is defined by their internal time base and lies in the timespan within which the preamble appears, the radio tags pass from a sleep state to an active state, and thereupon receive one of the data packets. The internal time base in the radio tags is corrected using the respectively received data packets and the deviation from the reference instant coded therein, so as to reset the next wakeup instant, and thereby maintain a synchronous state with the communication station. However, the preamble used has proven itself disadvantageous, because it produces a relatively high data volume.
The object of the invention is to provide a system that avoids the problems enumerated at the outset.